Astrophysical observables for regular black holes with sub-Planckian curvature

TL;DR

This paper studies the properties of photon spheres and stable orbits around regular black holes with sub-Planckian curvature, proposing observational methods to distinguish different black hole types.

Contribution

It introduces a detailed analysis of geodesic orbits and stability in regular black holes with Minkowskian cores, extending to horizonless compact objects and comparing with other black hole models.

Findings

Photon sphere and ESCO locations differ between Minkowskian and dS core black holes.

Massive particles exhibit double-valued ESCOs in CMO phase.

Potential observational signatures to distinguish black hole types.

Abstract

We investigate the photon sphere and the extremal stable circular orbit (ESCO) for massive particles over a recently proposed regular black holes with sub-Planckian curvature and Minkowskian core. We derive the effective potential for geodesic orbits and determine the radius of circular photon orbits, with an analysis on the stability of these orbits. We extend our analysis to the background of compact massive object (CMO) without horizon, whose mass is below the lowest bound for the formation of a black hole. For massive particles, the ESCOs become double-valued in CMO phase and we calculate the innermost stable circular orbits (ISCO) and the outermost stable circular orbits (OSCO). By comparing wih Bardeen black hole and Hayward black hole, it is also found that the locations of photon sphere and ESCO in CMO phase with Minkowskian core are evidently different from the ones in CMO phase with dS core, which potentially provides a way to distinguish these two sorts of black holes by astronomical observation.